Method and apparatus for determining temperature in a gas feedstream

ABSTRACT

An internal combustion engine includes an exhaust gas feedstream flowing past a gas sensing device disposed therein. The gas sensor includes an integrated electrical heating element which provides a resistance indicative of its temperature. An unknown input observer is used to determine the exhaust gas feedstream temperature based on the heating element temperature.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 11/853,074,filed Sep. 11, 2007, the contents of which are incorporated byreference.

TECHNICAL FIELD

This disclosure is related to monitoring temperature in a gasfeedstream.

BACKGROUND

Modern vehicles require exhaust aftertreatment systems and enginecontrol to achieve emissions levels to comply with various regulations.It is known that aftertreatment systems operate most efficiently undercontrolled conditions, including operating within appropriatetemperature windows. It is desirable to have information regarding anexhaust gas feedstream, including air/fuel ratio and temperature, atmultiple locations in an aftertreatment system which is equipped withmultiple reactors, catalysts or other emission abatement devices. It isknown that engine systems employing lean NO_(x) trap devices (LNT)operate most effectively to trap and regenerate when the LNT ismaintained within a narrow range of operating temperatures. It is knownthat diesel particulate filters (DPF) and selective catalyst reductionsystems operate most effectively within a narrow range of operatingtemperatures.

Known engine control systems utilize one or more gas sensing devices tomonitor the exhaust gas feedstream for feedback to the engine system foremissions control and diagnostics. Known gas sensing devices includeconventional oxygen sensors, wide-range air/fuel ratio sensors, andexhaust gas constituent sensors, e.g., NOx sensors. A gas sensing deviceincludes a sensing element and an electrically-powered integral heatingelement. The heating element is used to rapidly heat up and maintainoperating temperature of the sensing element within an optimum range ofoperational temperatures. The sensing element is adapted to monitoroxygen concentration, air/fuel ratio, or other exhaust gas constituents.Known internal combustion engines use one or more gas sensing devices tomonitor gases in an exhaust system, an exhaust gas recirculation (EGR)system, and an intake manifold, such as described.

Information regarding the temperature of the exhaust gas feedstream isuseful for controlling operation of the engine system to achieveemissions targets, since the effectiveness of a device that treatsexhaust gases is dependent upon the operating temperature of the deviceand the feedstream temperature. A known system for determining theexhaust gas feedstream temperature includes employing a temperaturesensor to monitor temperature at a specific location, with the sensorsignal output to an electronic control module which controls engineoperation. Such a system adds cost, while providing accuracy associatedwith direct measurement of temperature. Another known system fordetermining temperature of the exhaust gas feedstream includesalgorithms to estimate temperature based upon engine operatingconditions and information from existing sensing devices. Such a systemincurs limited cost to the system, but requires investment ofengineering resources to develop the algorithms and calibration.Furthermore, accuracy of the temperature estimation is known to vary.

SUMMARY

A gas feedstream temperature is measured by providing a gas sensingdevice including an integrated heating element disposed within the gasfeedstream. Electrical resistance of the integrated heating element ismeasured and temperature of the integrated heating element based uponthe measured electrical resistance is determined. A gas temperatureproximal to the sensing device is determined based upon the temperatureof the integrated heating element. And, the gas feedstream temperatureis determined based upon the gas temperature proximal to the sensingdevice.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments will now be described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of an exemplary engine and exhaustaftertreatment system in accordance with the present disclosure;

FIG. 2 is a partial sectional view of an exhaust gas sensing device inaccordance with the present disclosure; and,

FIG. 3 is a schematic view of an electrical circuit in accordance withthe present disclosure.

DETAILED DESCRIPTION

Referring now to the drawings, wherein the showings are for the purposeof illustrating certain exemplary embodiments only and not for thepurpose of limiting the same, FIG. 1 comprises a schematic diagramdepicting an internal combustion engine 10, exhaust aftertreatmentsystem, and control module 5 which are in accordance with an embodimentof the disclosure.

The engine 10 comprises a direct-injection internal combustion engine.The skilled practitioner understands that the disclosure applies to amultiplicity of engine configurations. During ongoing engine operation,combustion events occur during engine cycles when fuel is injected intocombustion chambers and ignited. In-cylinder burned gases are generatedwhich become exhaust gases when passed out of the combustion chamberwith opening of engine exhaust valves.

The exhaust gas feedstream is characterized by parameters including massflowrate, temperature, air/fuel ratio, and by concentrations of variousgas constituents, including waste products output from the combustionprocess of the internal combustion engine. The gas constituents caninclude unburned hydrocarbons, carbon monoxide, nitrides of oxygen,particulate matter, and other gases that are regulated by variousfederal or state emissions laws and regulations. The gas constituentsalso include other gases, e.g., oxygen and carbon dioxide. Thecharacterization of the gas feedstream in terms of states of theaforementioned parameters and constituents is known.

The exhaust aftertreatment system comprises an integrated system forconverting exhaust gas constituents. This comprises oxidizing unburnedhydrocarbons and carbon monoxide to oxygen and carbon dioxide, reducingnitrides of oxygen to nitrogen and oxygen, and combusting theparticulate matter to elemental carbon, among others. The exhaustaftertreatment system can be constructed of a plurality of devices whichemploy technologies having various capabilities for treating the exhaustgas constituents, including, e.g., three-way catalytic conversion, leanNOx adsorption and reduction, selective catalyst reduction, oxidation,and particulate filtering. The devices are preferably fluidly connectedusing pipes and connectors. An engine exhaust manifold entrains anddirects exhaust gas flow to the exhaust aftertreatment system. Theaftertreatment system as depicted comprises a first catalytic device 15′and a second catalytic device 15. Known catalytic devices comprise ametal housing device having a flow inlet and a flow outlet andcontaining a ceramic honeycomb-structure substrate impregnated with aplatinum-group metal catalyst supported on an alumina washcoat, althoughthe disclosure is not so limited.

The control module 5 comprises an electronic device adapted for use withthe engine 10. The control module 5 is signally connected to sensingdevices to monitor engine operation, and operably connected to actuatorsto control engine operation. The sensing devices are installed on ornear the engine to monitor physical characteristics and generate signalswhich are correlatable to states of engine and ambient parameters. Thesensing devices preferably comprise sensors including a crank sensor formonitoring crankshaft speed (RPM), a pressure sensor for monitoringintake manifold pressure (MAP) and ambient pressure (BARO), a mass airflow sensor for monitoring intake mass air flow (MAF) and intake airtemperature (T_(IN)), and, one or more gas sensing devices 20 formonitoring states of one or more parameters of the exhaust gasfeedstream, e.g., air/fuel ratio and exhaust gas constituents (EXH). Thegas sensing devices 20 are selectively placed in the exhaust systembefore, in the middle of, and after the aftertreatment devices 15, 15′for feedback control and diagnostics of the engine, the exhaust gasfeedstream and the aftertreatment devices. Alternatively, or inaddition, gas sensing devices may be adapted to monitor gases in an EGRsystem (not shown), or the engine intake manifold.

Actuators are installed on the engine and in the aftertreatment system,and are controlled by the control module 5 in response to the operatorinputs to achieve various performance goals. Actuators include, e.g., anelectronically-controlled throttle device which controls throttleopening to a commanded input (ETC), and a fuel injector adapted toinject fuel into engine combustion chambers in response to a commandedinput (INJ_PW), the EGR system, an ignition system to controlspark-ignition on systems so equipped, and other systems controlled inresponse to operator input in the form of an operator torque request(TO-REQ).

The control module 5 monitors inputs from the sensing devices,synthesizes pertinent information, and executes algorithms to controlvarious actuators to achieve control targets, including such parametersas fuel economy, emissions, performance, drivability, diagnostics, andprotection of hardware. The control module is operably connected, eitherdirectly or through the control system, to a plurality of devicesthrough which a vehicle operator controls or directs operation of thevehicle and powertrain. Exemplary devices through which the vehicleoperator controls or directs the operation of the powertrain include thethrottle and brake pedals, a transmission gear selector, and vehiclespeed cruise control. The engine is preferably equipped with othersensors (not shown) for monitoring operation and system control. Each ofthe sensing devices is signally connected to the control module 5 toprovide signal information which is transformed by the control module toinformation representative of a state one or more of the engine andambient parameters. It is understood that this configuration isillustrative, not restrictive, including the various sensing devicesbeing replaceable within functionally equivalent devices and algorithmswhich fall within the scope of the disclosure.

The control module 5 is preferably an element of a distributed controlsystem comprising a plurality of control modules adapted to providecoordinated control of the various vehicle systems including thepowertrain system described herein, when the engine is used in avehicle. The control module 5 comprises a central processing unitsignally electrically connected to volatile and non-volatile memorydevices via data buses. The control module is preferably ageneral-purpose digital computer generally comprising a microprocessoror central processing unit, storage mediums comprising random accessmemory (RAM), non-volatile memory devices including read only memory(ROM) and electrically programmable read only memory (EPROM), high speedclock, analog to digital (A/D) and digital to analog (D/A) circuitry,and input/output circuitry and devices (I/O) and appropriate signalconditioning and buffer circuitry. Control algorithms, comprisingresident program instructions and calibrations, are stored in thenon-volatile memory devices and executed to provide the respectivefunctions. Algorithms can be executed during preset loop cycles suchthat each algorithm is executed at least once each loop cycle.Algorithms are executed by one of the central processing units tomonitor inputs from the sensing devices and execute control anddiagnostic routines to control operation of the respective device. Loopcycles are executed at regular intervals, for example each 3.125, 6.25,12.5, 25 and 100 milliseconds during ongoing engine and vehicleoperation. Alternatively, algorithms may be executed in response tooccurrence of an event.

FIG. 2 schematically depicts the gas sensing device 20, preferablycomprising a planar-type heated sensing device, a portion of which isinserted into the exhaust gas feedstream. The gas sensing device 20comprises a sensing element 22 and a controllable heating element 24operably coupled to the control module 5. The output of the sensingelement 22 is input to the control module 5 for signal processing and todetermine a state of a parameter of the exhaust gas feedstream. The gassensing device 20 as shown is mounted in an exhaust pipe of the exhaustsystem on a mounting structure that preferably comprises a threadedmounting boss or another device suitable for mounting. The sensingelement 22 of the exemplary gas sensing device 20 comprises a zirconiumoxide element operable to monitor a partial oxygen pressure of theexhaust gas feedstream. Alternatively, the sensing element 22 maycomprise an element operable to monitor states of parameters of the gasfeedstream, including constituent elements, e.g., nitrides of oxygen(NO_(x)), carbon dioxide (CO₂), carbon monoxide (CO), or hydrocarbons(HC). The heating element 24 comprises a known electrical resistiveelement or a positive temperature coefficient electrical resistiveelement, and is electrically connected to the control module via anelectrical wiring harness, as depicted with reference to FIG. 3. Thereis a relationship between the resistance, R_(H), and a temperature ofthe heating element 24, T_(H), that is determined during development ofthe gas sensing device 20, is consistent from part to part, and can becalibrated during stasis periods using an on-system temperature, e.g.,T_(IN) from the intake air sensor. The temperature/resistancecalibration is stored in one of the memory devices of the control moduleto control temperature of the heating element. FIG. 2 depicts locationsof temperatures of interest for the disclosure, including: temperatureof the exhaust gas feedstream, T_(EXH); temperature of gases within alower shield surrounding the sensing element, T_(INT); temperature ofthe heating element 24, T_(H); temperature of an upper shieldsurrounding the sensing element, T_(up); and ambient temperaturesurrounding the upper shield, T_(A).

FIG. 3 depicts a schematic diagram of an exemplary circuit forcontrolling operation of the heating element 24. The circuit comprisesthe sensor 20 connected to the control module 5, including the heatingelement 24, a field-effect transistor (Power MOSFET), and a precisionreference resistor, R_(ref). The circuit further comprises a systemvoltage (V_(batt)) and ground (GND). The field-effect transistor iscontrolled by a pulsewidth modulated (PWM) signal output from controlmodule 5 (Heater Control PWM). Node A denotes a specific juncture in thecircuit at which control module 5 measures battery voltage (BatteryVoltage Sensing) for analysis purposes. Node B denotes a specificjuncture in the circuit at which control module 5 measures voltage fordetermining heater current (Heater Current Sensing). The control module5 controls the amount of electrical power to the heating element 24 bycontrolling the PWM signal. The PWM signal is preferably a square wavesignal that alternates between zero voltage and system voltage at agiven frequency. The amount of power to the heating element 24 isdetermined by the frequency of the PWM signal and percentage of timeduring each cycle that the voltage level is at the system voltage,referred to as the duty cycle. The control module 5 determines theresistance of the heating element 24 by measuring voltages at Node A andNode B when the heating element is powered. The heating elementresistance, R_(H), is calculated based upon the voltages at Nodes A andB and the resistance of the reference resistor, R_(ref), using a knownvoltage divider relationship.

A method is now described to estimate exhaust gas temperature, T_(EXH),at a location in the exhaust aftertreatment system. The methodpreferably comprises executable code consisting of one or morealgorithms stored and executed in the control module 5, and depicted ina non-limiting manner with the exhaust system of the exemplary engineillustrated and described herein. The exhaust gas temperature, T_(EXH),is of interest for control schemes and systems related to managing theexhaust gas feedstream entering into or discharging from one of theexhaust aftertreatment devices, entering the EGR system, entering aturbocharger system, and others.

An unknown input observer (UIO) model is implemented as an algorithm inthe control module 5. The UIO algorithm for this embodiment is developedand calibrated to regularly and ongoingly estimate exhaust gastemperature at a specific location in the exhaust aftertreatment systembased upon the measured temperature of the heating element 24 of the gassensing device 20. The UIO model comprises mathematically reconstructinga state of a dynamic system, e.g., the exhaust aftertreatment system,having inputs that are not directly or readily measurable.

A physical model of the system for describing a relationship betweentemperatures in the exhaust gas feedstream is provided with reference toEqs. 1 and 2:T _(INT) =f(T _(EXH) , T _(A) , {dot over (m)} _(TH))  [1]{dot over (T)} _(H) =pT _(H) +qV _(BATT) I _(H) DC+T _(INT)  [2]wherein T_(INT), T_(EXH), T_(A) and V_(BATT) are as previously defined,and {dot over (m)}_(TH) comprises mass air flow preferably measured bythe MAF sensor, I_(H) comprises current through the heater based uponthe heater resistance R_(H), DC comprises duty cycle of the PWM signal,and p and q comprise calibratable constants based upon a sampling rate.Thus, there is a relationship between exhaust gas temperatures insidethe lower shield of the sensor, T_(INT), and the exhaust gastemperature, T_(EXH), which is affected by factors related to heattransfer through the shield, ambient and underhood temperatures, andmass airflow rate of the exhaust gas feedstream, and other factorsrelated to heat transfer and the exhaust gas feedstream.

To develop a system executable in the control module, a discrete modelof the relationship between exhaust gas temperatures is developed, usingthe following definitions:

-   x(k)=T_(H)(k);-   u(k)=V_(BATT)I_(H)DC;-   v(k)=T_(INT)(k); and-   y(k)=T_(H)(k).

A discrete space model of Eqs. 1 and 2 is defined as Eqs. 3 and 4:x(k+1)=αx(k)+βu(k)+γv(k)  [3]y(k)=x(k)  [4]

The model format of Eqs. 3 and 4 is rewritten into a standard format ofEq. 5, below:x(k+1)=Ax(k)+Bu(k)+Dv(k)y(k)=Cx(k)  [5]

A linear system theory is applied to the above linear model of Eq. 5. Inthis estimation application, C=1 and, therefore y(k)=x(k).

A general UIO model based upon the above system comprises a linearsystem having an unknown input, v(k), at time period k, modeled as alinear function, as in Eq. 6 and 7:{circumflex over (x)}(k+1)=(α−L ₁ α−L ₂){circumflex over (x)}(k)+(β−L₁β)u(k)+L ₁ y(k)+L ₂ y(k+1)  [6]{circumflex over (v)}(k+1)=γ(y(k+1)−α{circumflex over(x)}(k)−βu(k))  [7]

The term {circumflex over (x)}(k) comprises an estimate of the truestate x(k). Terms L₁ and L₂ are design parameters calibrated based uponthe desired performance for the estimation response. The terms α, β, andγ are preferably determined for a specific system during preproductiontesting and calibration, and may be updated during ongoing operation.The term {circumflex over (x)}(k) can be considered as a filteredversion of x(k) that is based upon a noisy measure of y(k).

Thus, using the UIO estimation, i.e., Eqs. 6 and 7, the internaltemperature, T_(INT)(k)=v(k), is estimated during ongoing operationbased upon the heater temperature, T_(H). The internal temperatureT_(INT)(k) is used to determine the exhaust gas temperature, T_(EXH)(k),based upon other engine variables. An inverse function of Eq. 1, above,i.e., f⁻¹(T_(INT)), is calculated, as in Eq. 8:T _(EXH) =f ⁻¹(T _(INT) , T _(A) , {dot over (m)} _(th))  [8]

An estimated exhaust temperature can be obtained via Eq. 9, based uponEqs. 6, 7 and 8:{circumflex over (T)} _(EXH) =f ⁻¹({circumflex over (T)} _(INT) , T _(A), {dot over (m)} _(th))  [9]

Thus, for the calibrated system, the control module ongoingly executesthe algorithms to estimate the gas temperature at the predeterminedlocation based upon the observed temperature of the heater for theexhaust gas sensing device.

The disclosure has described certain preferred embodiments andmodifications thereto. Further modifications and alterations may occurto others upon reading and understanding the specification. Therefore,it is intended that the disclosure not be limited to the particularembodiment(s) disclosed as the best mode contemplated for carrying outthis disclosure, but that the disclosure will include all embodimentsfalling within the scope of the appended claims.

The invention claimed is:
 1. Method for measuring a gas feedstreamtemperature, comprising: providing a gas sensing device including anintegrated heating element and surrounded by a lower shield filled withthe gas, the sensing device disposed within the gas feedstream;measuring electrical resistance of the integrated heating element;determining temperature of the integrated heating element based upon themeasured electrical resistance; executing an unknown input observermodel to estimate a gas temperature within the lower shield surroundingthe sensing device based upon the temperature of the integrated heatingelement; and, determining the gas feedstream temperature based upon theestimated gas temperature within the lower shield surrounding thesensing device.
 2. The method of claim 1, wherein the unknown inputobserver model comprises a linear model.
 3. The method of claim 1,wherein the gas feedstream comprises post-combustion process exhaustgases.
 4. The method of claim 3, wherein the post-combustion processexhaust gases comprise exhaust gases from an internal combustion engine.5. Control system for monitoring an exhaust gas feedstream, comprising:a sensing device having an integrated heating element and surrounded bya lower shield filled with the gas; a control module monitoring anelectrical resistance of the integrated heating element, determining atemperature of the integrated heating element based upon the electricalresistance, using an unknown input observer model to estimate a gastemperature within the lower shield surrounding the sensing device basedupon the temperature of the integrated heating element, and determininga temperature of the gas feedstream based upon the gas temperaturewithin the lower shield surrounding the sensing device.
 6. The controlsystem of claim 5, wherein the unknown input observer model comprises alinear model.
 7. The control system of claim 5, wherein the controlmodule determining a temperature of the gas feedstream based upon thegas temperature within the lower shield surrounding the sensing devicecomprises the control module determining temperature of the gasfeedstream at a predetermined location based upon the gas temperaturewithin the lower shield surrounding the sensing device.
 8. The controlsystem of claim 5, wherein the sensing device having an integratedheating element comprises a planar-type exhaust gas sensing device. 9.The control system of claim 5, wherein the sensing device is configuredto monitor a partial pressure of oxygen.
 10. The control system of claim5, wherein the sensing device is configured to monitor a gasconstituent.
 11. The control system of claim 5, wherein the sensingdevice is configured to monitor nitrides of oxygen.
 12. Control systemfor monitoring an exhaust gas feedstream within an exhaust gasaftertreatment system, comprising: an integrated heating element of asensing device adapted to monitor the exhaust gas feedstream the sensingdevice is surrounded by a lower shield filled with the gas; a controlmodule monitoring electrical resistance of the integrated heatingelement of the sensing device, determining a temperature of theintegrated heating element based upon the electrical resistance,estimating a gas temperature within the lower shield surrounding thesensing device based upon the temperature of the integrated heatingelement using an unknown input observer model, and determining atemperature of the exhaust gas feedstream based upon the estimated gastemperature within the lower shield surrounding the sensing device. 13.The control system of claim 12, wherein the sensing device having anintegrated heating element comprises a planar-type exhaust gas sensingdevice.
 14. The control system of claim 13, wherein the sensing devicemonitors a partial pressure of oxygen.
 15. The control system of claim13, wherein the sensing device monitors nitrides of oxygen.